Temperature sensor

Abstract

A temperature sensor includes a constant current source and a transistor stack connected to the constant current source. The transistor stack includes a first transistor having a base connected to the constant current source and a collector coupled to a supply voltage. The collector of the first transistor is electrically isolated from the base of the first transistor. The transistor stack includes a second transistor connected to the first transistor. The second transistor has a collector connected to an emitter of the first transistor and has a base connected to the collector of the second transistor. The transistor stack includes an output node disposed between the constant current source and the base of the first transistor. A voltage of the output node is indicative of a temperature.

What is claimed is: 
     
       1. A temperature sensor, comprising:
 a constant current source; 
 a transistor stack connected to the constant current source, the transistor stack including:
 a first transistor having a base connected to the constant current source and a collector coupled to a supply voltage, the collector of the first transistor being electrically isolated from the base of the first transistor, and 
 a second transistor connected to the first transistor, the second transistor having a collector connected to an emitter of the first transistor and having a base connected to the collector of the second transistor; and 
 
 an output node disposed between the constant current source and the base of the first transistor, wherein a voltage of the output node indicates a temperature of the transistor stack. 
 
     
     
       2. The temperature sensor of  claim 1 , wherein a current gain of the first transistor is matched to a current gain of the second transistor. 
     
     
       3. The temperature sensor of  claim 2 , wherein the current gain of the first transistor is within 20% of the current gain of the second transistor. 
     
     
       4. The temperature sensor of  claim 1 , wherein the transistor stack includes a third transistor having a collector connected to an emitter of the second transistor, and including a base connected to the collector of the third transistor. 
     
     
       5. The temperature sensor of  claim 4 , wherein a current gain of the first transistor is matched to a current gain of the second transistor and a current gain of the second transistor is matched to a current gain of the third transistor. 
     
     
       6. The temperature sensor of  claim 5 , wherein the current gain of the second transistor is within 20% of the current gain of the third transistor. 
     
     
       7. The temperature sensor of  claim 1 , wherein the first and second transistors include diodes operating as parasitic bipolar transistor devices. 
     
     
       8. The temperature sensor of  claim 1 , wherein the first transistor or second transistor includes a triple well diode structure. 
     
     
       9. The temperature sensor of  claim 1 , including a second transistor stack connected to the constant current source, the second transistor stack including:
 a third transistor having a base connected to the constant current source and a collector coupled to a second supply voltage, the collector of the third transistor being electrically isolated from the base of the third transistor, and 
 a fourth transistor connected to the third transistor, the fourth transistor having a collector connected to an emitter of the third transistor and having a base connected to the collector of the fourth transistor; and 
 a second output node disposed between the constant current source and the base of the third transistor, wherein a second voltage of the second output node indicates a temperature of the second transistor stack. 
 
     
     
       10. The temperature sensor of  claim 9 , wherein the transistor stack is a different size from the second transistor stack and the voltage of the output node of the transistor stack is different from the second voltage of the second output node of the second transistor stack when the temperature of the transistor stack is equal to the temperature of the second transistor stack. 
     
     
       11. A temperature sensor, comprising:
 a constant current source; 
 a first transistor having a base connected to the constant current source, a collector of the first transistor being electrically isolated from the base of the first transistor, and 
 a second transistor having a collector connected to an emitter of the first transistor and having a base connected to the collector of the second transistor; and 
 an output node disposed between the constant current source and the base of the first transistor, wherein a voltage at the output node is at least partially determined by a temperature of the first transistor or the second transistor. 
 
     
     
       12. The temperature sensor of  claim 11 , wherein a current gain of the first transistor is matched to a current gain of the second transistor. 
     
     
       13. The temperature sensor of  claim 12 , wherein the current gain of the first transistor is within 20% of the current gain of the second transistor. 
     
     
       14. The temperature sensor of  claim 11 , including a third transistor having a collector connected to an emitter of the second transistor, and including a base connected to the collector of the third transistor. 
     
     
       15. The temperature sensor of  claim 14 , wherein a current gain of the first transistor is matched to a current gain of the second transistor and a current gain of the second transistor is matched to a current gain of the third transistor. 
     
     
       16. The temperature sensor of  claim 15 , wherein the current gain of the second transistor is within 20% of the current gain of the third transistor. 
     
     
       17. The temperature sensor of  claim 11 , wherein the first and second transistor include diodes operating as parasitic bipolar transistor devices. 
     
     
       18. A temperature sensor, comprising:
 a transistor stack configured to connect to a constant current source, the transistor stack including:
 a first transistor having a base configured to connect to the constant current source and a collector configured to couple to a supply voltage, the collector of the first transistor being electrically isolated from the base of the first transistor, and 
 a plurality of other transistors, each having a collector and an emitter with a collector-emitter conduction path there-between and having a base that is connected to the collector, wherein the collector-emitter conduction paths of the plurality of other transistors are connected in series between an emitter of the first transistor and a ground node, wherein a voltage produced at the base of the first transistor indicates a temperature value. 
 
 
     
     
       19. The temperature sensor of  claim 18 , wherein a current gain of each of the first transistor and the plurality of other transistors are each matched.